body{
    padding-top: 50px;
}
.content{
    position: relative;
    bottom: 0;
}
.content .left-nav{
    position:fixed;
    top:50px;
    bottom:0;
    width:180px;
    background-color: #333;
}
.content .right-content{
    position:absolute;
    left:180px;
}